The present invention relates to improvements in signal processing systems and more particularly to improved techniques for eliminating interference or otherwise undesirable signal components from serial data samples to be processed by Moving Target Indicator type radar system processors.
Signal processing equipment for Moving Target Indicator (M.T.I.) radar systems (and similar type processing systes) in general is designed to receive only particular desired information for evaluation. However, as is often the case, the desired information is not isolated by itself, but is found in the presence of unwanted signals. For systems of the type described, these unwanted signals generally take on the form of information that is correlated with prior information-data samples. In other words, it is often desirable to remove components of the signal that appear the same in each information-data sample (i.e., correlated).
The importance of extracting information of this nature (i.e., correlated) from incoming data samples is clear and well known in diverse applications of data processing, in addition to this requirement for M.T.I.-type radar systems. In particular, "sea clutter", or interference from returns from waves, "chaff" and wind driven interference are factors giving rise to the major portion of correlated signal components of data. For M.T.I. radar and similar type systems, it is obvious that it is the removal of correlated signal components that is desired.
Prior data processing systems of various types and especially M.T.I. type preprocessing systems, have attempted to utilize correlated components between successive prior data samples in modifying incoming data for further processing. But prior techniques generally employ either parallel canceller loops or series iterative loops which function in an equivalent manner. Parallel interactive loops are unsatisfactory because they have longer setting times than independent canceller loops and must employ reduced loop gain to prevent loop-to-lop oscillation. Generally, prior series iterative techniques include undesirable aspects arising from an excessive number of stages. This increases system size and cost, while at the same time reducing system reliability.
In the copending case of Lewis et al previously referred to, a technique is employed which does not resort to iterative parallel or interactive loop techniques. In comparison, the present technique generally requires a fewer number of canceller devices.
The present invention, under certain circumstances, allows design of preprocessing devices achieving essentially the same result as that obtainable by the just cited copending application, but with a fewer number of components. The circumstances referred to generally involve more limited ambient environmental operating conditions. The technique of the present invention not only uses a limited-iterative processing technique but is especially configured.
Accordingly, the present invention has been developed to overcome specific shortcomings of the above known and similar techniques, and to provide a data processing technique for minimizing or enhancing particular aspects of an incoming data sample through resort to extraction of correlated signal components presently received signal sample and prior samples.